Phase behaviour of quaternary systems containing carbohydrate surfactants–water–oil–cosurfactant

Carbohydrate surfactants, such as n-alkyl β-D-glucopyranosides (CMG1) or 1-desoxy-1-N-methyldecanamido-D-sorbite (mega10), are nearly insoluble in n-alkanes and ternary mixtures of surfactant–water–n-alkane produce emulsions. On adding a cosurfactant (butan-1-ol, octan-1-ol or phenol) the classical Winsor phase pattern, including middle-phase microemulsions, should appear. The experimental study of the formation and properties of microemulsion states in multicomponent systems containing carbohydrate surfactant–water–oily component–cosurfactant is described with particular emphasis on phase composition of co-existing phases with respect to comparable amounts of water and oily component in one phase using HPLC analysis and the microstructure of the microemulsion states applying dynamic light scattering and freeze fracture electron microscopy. The phase behaviour as a function of the cosurfactant concentration was investigated for different systems, varying the kind of cosurfactant, the tail length of the surfactant, the chemical nature of the polar head group and the polarity of the oily component. The experiments were carried out at constant temperature, at constant surfactant concentration in the feed phase and at constant water-to-oil ratio in the feed phase. The most striking experimental observation is that adding a cosurfactant to a carbohydrate–water–oil mixture promotes the formation of microemulsion structures for all investigated systems, except for the system n-decyl β-D-glucopyranoside (C10G1)–water–n-octane–octan-1-ol. An important property of microemulsions is the ability, under carefully chosen conditions, to incorporate very large amounts of oil and water into homogeneous solutions.